The fact that the material under the solid surface is liquid is shown by the lava flows from volcanoes. Rocks are buried very deep in the earth’s crust under big mountains and in subduction zones. Under such conditions they suffer a number of changes. As they sink deeper into the crust, the earth’s internal activity leads to a rise in temperature. At the same time, the weight of the overlying rocks and mountains leads to a further tremendous increase in pressure. Matter is organised in specific combinations of elements which in the solid state form crystals called minerals. Different minerals come together to form rocks. Every rock has a combination of minerals, and every mineral has a unique combination of elements in a specific crystal form. The changes in temperature and pressure cause changes in the chemistry of most minerals through the substitution of one element for another. While some minerals, within certain limits, remain stable, at a critical point, matter is reorganised in different crystal forms. This causes a qualitative change in the minerals, which react, producing a new combination reflecting the new conditions. This is a qualitative leap, like the change of water to ice at 0°C. The result is that the entire rock is transformed into a new rock. Thus, under the pressure of environmental conditions, we have a sudden leap, involving a metamorphosis not only of minerals but of the rocks themselves. There is no one single mineral form that remains stable under all natural conditions.

In zones which experience the subduction of an ocean under a continent, rocks can be buried very deep in the crust. Under such extreme conditions, the rocks themselves begin to melt. However, this process does not happen all at once. We have the phenomenon of partial melting, because different minerals melt at different points. The melting material has a tendency to move upwards, since it is less dense than the surrounding rocks. But this movement is not without problems, owing to the resistance of the overlying rocks. The molten rock, or magma, will slowly move upwards until, faced with a solid barrier, it is temporarily forced to halt. In addition, the outer area of the magma will start to cool and consolidate into a solid layer that will act as an additional barrier in the path of the magma. But eventually, the elemental force of pressure from below gradually increases to a point where the barriers are broken, and the magma finally breaks through to the surface in a violent explosion, realising colossal pent-up forces.

It is therefore evident that these processes do not take place in an accidental way, as it may appear to the unfortunate victims of an earthquake, but correspond to fundamental laws, which we are now only beginning to understand. They take place in specific zones, located at the borders of the plates, especially in mid-ocean ridges and behind subduction zones. This is exactly the reason why there are active volcanoes in Southern Europe (Santorini in Greece, Etna in Italy), in Japan, where there are subduction zones (which led to the Kobe earthquake), in mid-Atlantic and the Pacific Ocean (volcanic islands and submerged volcanoes in mid-ocean ridges) and in East Africa (Kilimanjaro) where there is a continental drift and the creation of a new ocean.

It is well known to miners that the temperature of the earth’s crust increases the further down you go. The main source of this immense heat, which is responsible for all the processes that take place in the bowels of the earth, is heat energy released by the decay of radioactive elements. Elements contain isotopes (atoms of the same element, but with different mass), some of which are radioactive – that is to say, they are unstable and break down with time – producing more heat and more stable isotopes. This continuous process of reaction is proceeding very slowly, because these isotopes have been decaying since the origin of the earth, when they must have been more abundant. Thus, heat production and heat flow must have been higher than at present, maybe two or three times more during the Archaean period than now.

The Archaean-Proterozoic boundary is likewise of major significance, representing a qualitative leap. Not only do we have the emergence of the first life-forms, but also another crucial change in the land mass – from many small continental plates in the Archaean, with its numerous plate collisions, to the formation of larger, thicker and more stable plates during the Proterozoic. These large continental masses were the result of the aggregation of many small proto-continental plates. This was the period of major mountain building, of which two major episodes can be distinguished – 1.8 billion and one billion years ago. The remnant of the last event of this titanic process, in which the rocks were repeatedly metamorphosed, deformed and re-shaped, can be seen today in South Canada and North East Norway.

The gradualist theory of uniformitarianism, originally advanced by Hutton in 1778, has no application whatsoever to the early history of the earth. All the available evidence suggests that modern-style plate tectonics began in the early Proterozoic, whilst some earlier variant of the plate tectonic process seems most likely to have been in operation in Archaean times. More than 80 per cent of the present continental crust was created before the end of the Proterozoic period. Plate tectonics is the determining factor in all these processes. Mountain building, earthquakes, volcanoes and metamorphosis are all interconnecting processes, one depends on the other, each determines, influences, causes or is caused by the other, and all of them, taken together, constitute the evolution of the earth.